One of radio communication methods utilized in a mobile communication system is the OFDMA scheme. In the OFDMA scheme, carriers assigned to each base station are divided into multiple subcarriers which are orthogonal to each other. Further, the subcarriers are grouped by a predetermined number. The groups are referred to as sub-channels.
A frame of the OFDMA scheme is formed of multiple sub-channels. A region in the frame is specified by a combination of one or more sub-channels and symbols. A communication device (such as a mobile station device or a base station device) that attempts to transmit communication data transmits communication data by selectively using an intra-frame region (See Patent Document 1, for example).
In the mobile communication system, intra-frame regions to be respectively used by the base station device and the mobile station device for transmitting communication data, are both determined by the base station device. In order to notify the mobile station device of content of the determination, the base station device utilizes information called MAP. The MAP is intra-frame region specifying information for specifying a region in a frame that the base station device or the mobile station device uses for transmitting the communication data.
The base station device notifies the mobile station device of the MAP. From the notified MAP, the mobile station device recognizes an intra-frame region containing communication data that the base station device has transmitted to the mobile station itself, and an intra-frame region that the mobile station device will use when transmitting the communication data to the base station device. The notification of the MAP in WiMAX, which is one of the mobile communication systems adopting the OFDMA scheme, will be described in detail hereinafter.
FIG. 5 is a diagram showing an example of a frame configuration of the WiMAX. As shown in FIG. 5, in addition to the OFDMA scheme, the TDD (Time Division Duplex) scheme is adopted in the WiMaX, and a frame is divided into a downlink frame (DL) and an uplink frame (UL) according to time. The DL and UL are transmitted alternately. A frame consists of a DL and an UL following the DL. The MAP of the WiMAX contains intra-frame region specifying information for all mobile station devices which are in communication with the base station device. The base station device transmits the MAP by containing it in a specifying region of the DL (a leading part of the DL in FIG. 5).
When receiving the DL, the mobile station device first refers to the specifying region in the DL described above, and acquires the MAP contained in the specifying region. Then, the mobile station device retrieves MAP for the mobile station device itself from the acquired MAP. Next, according to DL-MAP of the MAP for the mobile station device itself, the mobile station device acquires an intra-frame region in the DL where communication data addressed to the mobile station device itself exists. Similarly, according to UL-MAP, the mobile station device acquires an intra-frame region in the UL that may contain communication data to be transmitted.    Patent Document 1: Japanese Patent Translation Publication No. 2005-535167, paragraph 0017